An ad-hoc network is a technique for self-configuring a communications network with multiple communications equipment sets that operates without a specific control station.
A wireless ad-hoc network is adapted to realize the ad-hoc network technique using radio links or wireless links in the mobile environment, and many studies and much research have been conducted regarding to the wireless ad-hoc network.
It is proposed to introduce the concept of a spanning tree, which is generally used in a wired network, into a wireless ad-hoc network when connecting communications apparatuses or access points via wireless links. (See, for example, JP 2000-69046A publication.) It is also proposed to prevent a loop to avoid wasteful packet relay when creating a spanning tree in a wireless network. (See, for example, JP 2000-78147A publication and JP 2003-188811A publication.)
Since ad-hoc networks are established in a self-configuring manner by communications apparatuses, if workload is concentrated on a specific communications apparatus, the influence spreads to all the apparatuses that transmit and receive data via that specific communications apparatus. In the above-described publications JP 2000-69046A and JP 2000-78147A, workload concentrates on a specific wireless base stationbase station located at the root of the tree, and therefore, the throughput of the entire network is reduced.
On the other hand, JP 2003-188811A proposes to maintain the communication quality by not establishing a channel with respect to a wireless base stationbase station with a low receive-power level when creating a tree. However, this method is not capable of calculating a link cost reflecting adaptive changes in communication rate in the wireless environment. Consequently, the throughput of the entire network cannot be improved.
To avoid the concentration of workload on specific equipment, it is proposed to use the workload on a communications apparatus as an indicator when performing routing control in an ad-hoc network. See, for example, Sung-Ju Lee and Mario Gerla, “Dynamic Load-Aware Routing in Ad hoc Networks”, Proc. ICC 2001, June, 2001. Also, see Hakoda, et al. “Performance Evaluation of Mobile Ad Hoc Routing Protocols Based on Link Expiration time and Load of Node”, IEICE Journal, Vol. 85-B, No. 12, 2002.
It is also proposed to switch between a link cost, which represents communication available time between terminals, and a node cost, which represents the busy rate of a terminal, depending on the network traffic. See Takahashi, et al., “Metric Selection Mobile Ad Hoc Routing Protocol Based on Link and Node Costs”, Technical Report of IEICE, NS 2003-80, RCS2003-103 (2003-7) at 67-72.
With the above-described conventional techniques, load distribution cannot be realized in the network. Or, even if workload is dispersed, efficient use of radio resources cannot be realized.